package com.joe.bitmap;
import Android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.graphics.Bitmap.Config;
import android.util.Log;
public class BitmapUtils {
private static final String TAG = "BitmapUtils";
/**
* Set the pixels's alpha. alpha's value decrease by the bit's height
* @param pixels
* the array which contains pixels.
* @param srcWidth
* the bitmap's width
* @param srcHeight
* the bitmap's height
* @param alphastart
* the first pixels's alpha
* @param percent
* the line's fouction's slope (y = mx+b;)
* such as: alphastart=0x2fffffff;(alpha's value 0x2f)
* m = 0x2f/(height * percent) (if the shadow fill full of the
* bitmap,k =1. otherwise the shadow only in a half of the bitmap
* percent = 0.5) alpha = m*height + alphaLagest
* The percent max value are 1!
* @param b
* the line's fouction's const (y = mx+b)
*/
public static void shadowFromPixels(int[] pixels, int srcWidth,
int srcHeight, int alphastart, float percent) {
int b = alphastart;
//if need display a part of (such as 1/2,1/3...) bitmap
int alpahLine = (int) (srcHeight * percent);
float temp = (alphastart >>> 24);
percent = ((temp / (srcHeight * percent)));
int alpha = 0;
Log.d(TAG, "shadowByPixels: percent=" + percent + "\tb=" + b
+ "\t temp=" + temp + "\tsrcHeight=" + srcHeight);
for (int i = 0; i < srcHeight; i++) {
if(i < alpahLine){
alpha = b - (((int) (i * percent)) << 24);
}else{
alpha = 0x00ffffff;
}
for (int j = 0; j < srcWidth; j++) {
pixels[j + i * srcWidth] = pixels[j + i * srcWidth] & alpha;
}
}
}
/**
* Set the pixels's alpha. alpha's value decrease by the bit's height
*
* @param pixels the array which contains pixels.
* @param srcWidth the bitmap's width
* @param srcHeight the bitmap's height
* @param alphastart the first pixels's alpha
*/
public static void shadowFromPixels(int[] pixels, int srcWidth,
int srcHeight, int alphastart) {
int b = alphastart;
float temp = (alphastart >>> 24);
float percent = (temp / srcHeight) ;
int alpha = 0;
Log.d(TAG, "shadowByPixels: percent=" + percent + "\tb=" + b
+ "\t temp=" + temp + "\tsrcHeight=" + srcHeight);
for (int i = 0; i < srcHeight; i++) {
alpha = b -(((int) (i * percent)) << 24);
for (int j = 0; j < srcWidth; j++) {
pixels[j + i * srcWidth] = pixels[j + i * srcWidth] & alpha;
}
}
}
//我的这个 算法有点问题:
我只考虑到 图片中每一行的alpha值是相同的,大多数图片是这样,但是有些图片不是哦.
这里是把每一行的alpha值,重新设置成了一个值,这是不能通用的.
通用的做法是把 这行的alpha值取出来,乘以一个比例
当前行号 = a,(0~a总)
需要显示总的行号 = a总
